The present invention relates to stereo signal processing and in particular to processing a stereo signal to create the impression of a wide sound stage and/or of immersion.
Conventional stereo reproduction, for example television, two-channel speakers such as iPod® speakers, etc., create an impression of a narrow spatial image. The narrow imaging is primarily due to loudspeaker proximity relative to each other and unmatched speaker-room frequency responses. The goal of any multichannel system is to give the listener an immersive or a “listener-is-there” impression. Unfortunately, narrow stereo imaging precludes such an experience.
The spatial resolution (i.e., localization ability) of human hearing is at least one degree. It is desirable to manipulate stereo signals to enlarge the stereo sound field and imagery by combining concepts from physical acoustics (for example, room acoustics of the space the listener is located in), signal processing (for example, digital filtering), and auditory perception (for example, spatial localization cues). Stereo expansion will allow listeners to perceive audio signals arriving from a wider speaker separation with high-fidelity through the use of a unique binaural listening model and speaker-room equalization technique.
Known stereo signal combining approach (for example, L+α(L−R) and R+α(R−L)) have attempted to expand the acoustic field. Unfortunately, these often result in vocals “drowned out” & midrange coloration. Also, benefits from speaker-room equalization cannot be incorporated because the stereo signal combining is independent of room equalization. Other methods include Head-Related-Transfer-Functions (HRTFs) premised on the localization ability of the human pinna (the visible portion of the ear extending from the side of the head which colors sound based on the arrival angle). However, human pinna vary among listeners and an expansion approach, involving use of specific direction HRTF, is not robust, and equalization is again defeated.